Vessel-mounted ocean thermal energy conversion system

ABSTRACT

An offshore power generation system comprising: a floating portable platform having one or more OTEC heat exchange units, one or more turbine generators, a water intake and discharge system, a mooring system; and a fixed manifold having one or more cold water intake connections in communication with a cold water pipe, and one or more cold water discharge connections in communication with the water intake system of the floating platform via an intermediate cold water conduit, wherein each cold water discharge connection is detachable from the intermediate cold water pipe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation {continuation or continuation-in-partor divisional} application of and claims priority to U.S. applicationSer. No. 15/112,781, filed on Jul. 20, 2016, which is the US NationalPhase of International Application Serial No. PCT/US2015/012102, filedon Jan. 20, 2015, which claims priority to U.S. Application Ser. No.61/929,210, filed on Jan. 20, 2014. The entire disclosure of eachapplication is hereby incorporation by reference.

TECHNICAL FIELD

This invention relates to Ocean Thermal Energy Conversion (OTEC) plants,and more particularly to floating OTEC plants.

BACKGROUND

Ocean Thermal Energy Conversion (“OTEC”) is a manner of producingrenewable energy using solar energy stored as heat in the oceans'tropical regions. Tropical oceans and seas around the world offer aunique renewable energy resource. In many tropical areas (betweenapproximately 20° north and 20° south latitude), the temperature of thesurface sea water remains nearly constant. To depths of approximately100 ft the average surface temperature of the sea water variesseasonally between 75° and 85° F. or more. In the same regions, deepocean water (between 2500 feet and 4200 feet or more) remains a fairlyconstant 40° F. Thus, the tropical ocean structure offers a large warmwater reservoir at the surface and a large cold water reservoir atdepth, with a temperature difference between the warm and coldreservoirs of between 35° to 45° F. This temperature difference remainsfairly constant throughout the day and night, with small seasonalchanges.

The OTEC process uses the temperature difference between surface anddeep sea tropical waters to drive a heat engine to produce electricalenergy. OTEC power generation was identified in the late 1970's as apossible renewable energy source having a low to zero carbon footprintfor the energy produced. An OTEC power plant, however, has a lowthermodynamic efficiency compared to more traditional, high pressure,high temperature power generation plants. For example, using the averageocean surface temperatures between 80° and 85° F. and a constant deepwater temperature of 40° F., the maximum ideal Carnot efficiency of anOTEC power plant will be 7.5 to 8%. In practical operation, the grosspower efficiency of an OTEC power system has been estimated to be abouthalf the Carnot limit, or approximately 3.5 to 4.0%. Additionally,analysis performed by leading investigators in the 1970's and 1980's,and documented in “Renewable Energy from the Ocean, a Guide to OTEC”William Avery and Chih Wu, Oxford University Press, 1994 (incorporatedherein by reference), indicates that between one quarter to one half (ormore) of the gross electrical power generated by an OTEC plant operatingwith a ΔT of 40° F. would be required to run the water and working fluidpumps and to supply power to other auxiliary needs of the plant. On thisbasis, the low overall net efficiency of an OTEC power plant convertingthe thermal energy stored in the ocean surface waters to net electricenergy has not been a commercially viable energy production option.

Environmental concerns associated with an OTEC plant have also been animpediment to OTEC operations. Traditional OTEC systems draw in largevolumes of nutrient rich cold water from the ocean depths and dischargethis water at or near the surface. Such discharge can effect, in apositive or adverse manner, the ocean environment near the OTEC plant,impacting fish stocks and reef systems that may be down current from theOTEC discharge.

SUMMARY

Vessel-mounted OTEC plants are optimally moored on station and provideelectricity to the grid 24 hours a day, 365 days a year. The platformsupports and protects machinery and operating personnel but must be ableto survive in severe ocean storms. In the case of 2-10 megawatt floatingproduction plants that would serve small commercial markets, a sea-goingbarge is the best platform. Its relatively large size supports the bulkymultiple component OTEC machinery at a reasonable capital cost whileproviding a relatively stable and survivable platform for OTECoperations. The personnel have access for inspection and repair, whichwould be impossible with a scaled-down spar.

In an example implementation of the present invention, an offshore powergeneration system comprises a floating portable platform having one ormore OTEC heat exchange units, one or more turbine generators, a waterintake and discharge system, and a mooring system. The offshore powergeneration system also comprises a fixed manifold including one or morecold water intake and/or return connections in communication with coldwater pipe(s); one or more cold water discharge connections incommunication with the water intake and/or return system of the floatingplatform via an intermediate cold water conduit, wherein eachintermediate cold water discharge pipe connection is detachable from themanifold, and each discharge pipe connection of the discharge piperunning from cold water intake and running to cold water discharge depthis detachable from the manifold. The fixed manifold may also include awarm water return system including one or more warm water returnconnections in communication with warm water pipes; one or more warmwater discharge connections in communication with the water returnsystem of the floating platform via an intermediate warm water conduit,wherein each warm water discharge connection is detachable from theintermediate warm water pipe, and a warm water discharge pipe runningfrom the manifold to an open end at discharge depth that is detachablefrom the manifold. In some cases, the manifold itself is segmented intowatertight boundaries for each type of flow: cold water intake, coldwater return and warm water return. In some cases, the cold water returnand warm water return pipes running from the manifold to return depthrun parallel, are banded together and discharge at the same depth toprovide mixing of flows.

Other example implementations of the present invention may include oneor more of the following features. Some system have one or more OTECheat exchange units comprising a multi-stage cascading hybrid OTEC heatexchange system. In some systems, each OTEC heat exchange unit isconnected to the water intake and discharge system to allow forsubstantially linear flow of cold water and hot water across the OTECheat exchange unit. In some systems, each OTEC heat exchange unitcomprises a plurality of heat exchange plates positioned in the flowpath of the cold water supply. In some systems, each OTEC heat exchangeunit comprises a plurality of heat exchange plates positioned in theflow path of the warm water supply. In some systems, an OTEC workingfluid flows through an interior passage of one or more heat exchangeplates, each heat exchange plate surrounded by and in the flow path ofthe cold or warm water supply. In some systems, each OTEC heat exchangeunit comprises four cascading heat exchange zones. In some systems, eachcascading heat exchange zone arranged to facilitate horizontal flow ofthe cold or warm water supply. In some systems, the water intake anddischarge system comprises a warm water supply pump and a cold watersupply pump. In some systems, the water intake and discharge systemincludes a warm or cold water discharge pump.

In some cases, there are only the intake pumps as all the pumping powerneeded to flow the water through the system—from intake opening toreturn opening—is performed by the intake pump(s). There may be morethan one primary seawater pump for warm and cold seawater systems. Forexample, there can be at least one and possibly more dedicated warmwater seawater pumps for each evaporator chamber, and at least one andpossibly more dedicated cold water primary seawater pumps for eachcondenser chamber. Multiple pumps provide redundancy so that, forexample, if a pump should need maintenance, but none is required of theheat exchangers at the time, water can be flowed through the heatexchanger chamber with minimal net power output reduction. Because thepump intakes are at or below sea level, the design reduces head pressurerequirements, so smaller motors with lower parasitic loads can be usedto drive pumps large enough to accomplish this work.

In some systems, one or more discharge pipe(s) is (are) in communicationwith the discharge of the water intake and discharge system(s). In somesystems, the intermediate cold water pipe(s) is (are) detachable fromthe water and intake discharge system. In some systems, the intermediatewarm water pipe(s) is (are) detachable from the water discharge system.In some systems, the discharge pipe(s) is (are) detachable from thewater intake and discharge system. In some systems, the terminal end ofthe warm water discharge pipe is open at a depth between 25 and 300 feet(e.g., between 250 and 600 feet). In some systems, the terminal end ofthe cold water discharge pipe is open at a depth between 25 and 600 feet(e.g., between 250 and 600 feet). In some systems, the terminal end ofthe warm water and cold water discharge pipes discharge water at a depthhaving a temperature within 10 degrees Fahrenheit of the ambient water.Some systems also comprise a cold water discharge pipe in communicationwith the water intake and discharge system and the fixed manifold; awarm water discharge pipe in communication with the water intake anddischarge system and the fixed manifold; wherein the warm and cold waterdischarge are mixed in the fixed manifold and discharged from themanifold at a temperature within 10 degrees Fahrenheit of the ambientwater.

In some cases, where the flows and pressures are not the same, this cancreate a differential head from one system that can interfere with theflow of the other system, possibly preventing the system from operatingas intended. In some cases, the fixed manifold has separate chambers forwarm and cold water discharges. The flows discharge at the same depthand are nozzled so that the flows cross and mix in the open oceaninstead of inside a single chamber. By allowing each system to operateindependently, each system can be sized appropriately to reduce powerrequired.

Some systems comprise mixing nozzle(s) in communication with the warmand cold water discharge(s). In some systems, the cold water pipe iscoupled directly to the water intake and/or discharge system via a coldwater pipe connection. Some systems comprise an auxiliary cold watersupply exiting the heat exchanger and flowing to an auxiliary fixedmanifold and supplying an auxiliary system. In some systems, theauxiliary system is a shore based air conditioning system or adesalination system or a combination of both systems.

In yet another example implementation of the present invention, a methodof power generation within the littoral offshore zone comprises thesteps of: providing a portable floating OTEC power generation station,wherein the floating OTEC power generation station comprises; one ormore OTEC heat exchange units;

one or more turbine generators; a water intake and discharge system; anda mooring system; fixing a water intake manifold to the sea floor at adepth between 30 and 450 feet; connecting a cold water pipe to the fixedwater intake manifold; connecting an intermediate cold water pipebetween the fixed water intake manifold and the water intake anddischarge system of the floating OTEC power generation station.

Various implementations of the present invention present one or more ofthe following advantages:

Vessels, e.g., barges, of the size needed for this application areeasily constructed in most coastal nations, enabling commercializationof this technology globally.

Barges can easily be built in one location and towed to the operatingsite, thereby facilitating broad use of this technology, even at remoteislands.

A barge-mounted OTEC plant, as with any power barge, can provideelectricity to remote communities isolated from a major power grid,enabling local electrification and development.

Barges take advantage of the island and near-island geological formationwith a narrow, shallow shelf and a very steep escarpment that drops togreat depths. Mooring in deep water is difficult and expensive comparedto the amount of energy required. Operating from land involves cuttingvery wide swaths of 40 feet to 60 feet through the reef for the fourwarm and cold water intake and return pipes. By mooring in the shallowshelf close to the drop off, barge-mounted OTEC plants are able to:

-   -   a) use relatively short lengths of commercially available HDPE        pipe to extract and return cold seawater and warm seawater;    -   b) stay in the lee of land for reduced wind and wave effects    -   c) use a shorter run of power cable to shore, with minimal        impact to the reef, deployed and reefed from a service barge        instead of a specialty cable laying ship from the other side of        the world    -   d) moor in shallower water at depth divers routinely work    -   e) moor using commercially available anchoring systems (not        customized) installed from a service barge instead of a        specialty mooring ship from thousands of miles away    -   f) provide a stable platform for the power generating equipment    -   g) provide jobs for the local economy during site development,        through construction and installation, and during operation    -   h) be built in many shipyards around the world (does not require        a large dry-dock or construction basin with mega-lift capacity        crane service    -   i) use systems, sub-systems and components that are commercially        available stock items with pedigrees and technical data, a        proven support infrastructure, and global warehousing for speedy        replacement, if needed, and for which the lowest replaceable        units are sized such that they can be shipped by common truck,        or air carrier.

A barge is an excellent platform for efficient flow of seawater andworking fluid for the net power output of 2.5 megawatts to 5.0 megawattsrequired by a very large number of island communities.

The barge design, with the moon pool in the center, uses the hull toscreen out flotsam and jetsam by shielding the intake. The moon poolalso minimizes surface turbulence in the immediate area of the intakeand minimize risk of “gulping” air and the insulative nature andtemperature of the hull surrounding the moon pool helps to negatethermal effects of rain and surface mixing during storms;

In many island communities with an average maximum demand of 100 to 200megawatts, there is a very high risk of power grid disruption if asingle 25 MW or larger (25% or more of the demand load) generating planttrips off line (as could happen if a ship anchor drops onto thesubmarine power cable of an OTEC plant moored farther from shore).Several 5 MW OTEC barges can be dispersed around the island, tying intothe grid at various points, to provide system redundancies and helpensure transmission and distribution stability and speedy disasterrecovery.

The barge-mounted OTEC plant will be located close to shore (typicallyone mile or less from shore), out of shipping lanes, in waters typicallyshallower than pelagic fishing occurs in, yet returns seawater thatenhances the food chain to a depth just offshore where local fishermencan benefit.

The barge is moored in relatively shallow water. This opens theopportunity to seek services from more ocean surveyors, constructionfirms, divers, tug and supply barge services, including local instead ofglobal companies, thereby creating jobs for the local economiesthroughout the planning and construction phases and making OTEC projectsmore economically viable.

The 5 MW OTEC plant produces lower voltage power that is transmitted toshore in a smaller diameter submarine power cable. The HorizontalDirectional Drilled bore-hole is smaller in diameter, having lower costof installation and impact on the environment. The cable is lower cost,and being such a short run from shore in relatively shallow water, canbe easily retrieved and repaired if necessary. A replacement cable canbe deployed and installed, if needed, in relatively short time by acommercial tug and barge service firm without the need for a specialtycable-laying ship.

The mooring system for the barge-mounted OTEC plant is significantlysmaller in scale than for a spar. The mooring anchors are set inrelatively shallow water, a process that can be and is routinely done bycommercial tug and barge service firms, such as Healy-Tibbitts. Aspecialty mooring ship is not required.

Because the barge is so close to shore, consumable supplies can betransported to the plant by boat. There is no need for helicopterservices. Because of this, there is no need for special helicopterdesign and certification on the barge.

The barge, with the 8-point moor, provides a highly stable platform forthe OTEC machinery, so commercial-grade power equipment that is readilyavailable from many suppliers around the world can be specified andsupplied quickly and competitively, while ensuring best value andeconomic viability.

The barge and fixed manifold address the problem of excessive motion ofthe platform stressing and prematurely failing the cold water pipe. Byusing several smaller diameter but more flexible commercially availablestandard size HDPE risers from the platform to the fixed manifold, setand anchored to the sea floor well below the wave forces at the surface,then large diameter commercially available HDPE pipes from the manifoldto terminal depths, the cold water intake and cold water and warm waterreturn pipes are more survivable. Multiple risers of each type of flowprovide redundancy. The risers can be detached and anchored to the seafloor prior to a severe storm, such as a Category 3 or higher hurricane,then quickly retrieved and reattached so that operation can be restoredand power to the utility grid quickly reenergized for speedy disasterrecovery. By using standard size, commercially available HDPE pipes,with technical data available attesting to performance characteristics,overall project risk is mitigated while costs are predictable andconstrained. The support system is already in place.

In the event of severe storms (e.g., a Category 3 or higher hurricane),the barge can be detached from the seawater pipes and moorings and towedto safe harbor. Modern weather forecasting, aided by satellite imageryand hurricane chasing airplanes, can usually provide several dayswarning of severe tropical storms, enough time to take suchprecautionary action.

The barge provides large, open deck area for operations and maintenance.Equipment can easily be removed, moved, repaired or replaced, and thesystem restored quickly and efficiently. This openness also facilitateseasier and speedier installation of equipment at a lower cost thaninstallation in a confined and cramped space such as a spar.

The sizes of the system components comprising the power block and marinesystems of the 5 MW OTEC plant are such that common, off-the-shelf stockpiping, valves and fittings can be used, for which a competitive pricingand support structure already exist, thereby minimizing manufacturing,assembly, operation and cost risks.

The main deck of the barge can be fully encapsulated using a curvedcovering, much like a Quonset hut structure, to prevent direct sunlightand rain from striking the surfaces of the equipment housings, therebyreducing maintenance requirements, prolonging their service life, andlowering operating costs. The enclosure also serves as a barrier torelease of ammonia vapor in the event of a major leak. Ammonia gas isgiven off more easily from an aqueous solution as the temperatureincreases, so the deck covering will hold the vapors inside while thewater mist system, attached to the underside of the structure of thedeck covering, captures the ammonia in an aqueous solution that can bedrained into tanks in the hull, and from which the anhydrous ammonia cansafely be extracted and recycled. The curved deck covering also providesa smooth slip stream for wind in a storm, much like the leading edge ofan airplane wing. Lastly, the barges can be painted so that itsappearance blends smoothly in with the surrounding sea and sky so thatthe barge may pose minimal visually intrusion due to its proximity toshore.

Two major challenges of small commercial OTEC systems on a barge orsmaller vessel are the long-term performance of the CWP connection tothe platform and the survivability of the platform with quick return toservice in severe storm conditions. The disclosed design reduceconnection stresses and mitigate these critical risks: (1) by insertingthe manifold thus providing a “two-step” connection from the long 3000+feet CWP to a manifold and then from the manifold 25 feet to 300 feet tothe platform; (2) by using smaller, more flexible piping in the higherstress shallow region from the platform to the manifold and stronger,more rigid and larger pipe for manifold to the deep water intake andreturn; and (3) designing the capacity to detach the pipes from theplatform to the manifold in severe hurricane conditions, shutting downoperations in a controlled process, with the ability to quicklyre-attach after the storm, rather than suffer pipe breakages at theconnection point.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are, respectively, perspective and end views of anexemplary OTEC plant.

FIG. 2 is a plan view of the OTEC plant of FIGS. 1A and 1B.

FIGS. 3 and 4 are plan views of the main deck and lower deck,respectively, of a barge-mounted OTEC plant including a moon pool.

FIGS. 5-7 are diagrams of a portion of the piping of the barge-mountedOTEC plant of FIGS. 3 and 4.

FIGS. 8 and 9 are schematics of an OTEC plant configured to provideonshore seawater air-conditioning.

FIG. 10 is a perspective view of a portion of the mooring system.

FIG. 11 is a schematic illustrating adjustments of a mooring system withchanging sea level.

FIG. 12 is a perspective view of a mooring system and cold water pipeconfiguration for a barge-mounted OTEC plant.

FIGS. 13 and 14 are end views of collar anchors for piping.

FIGS. 15-17 are schematic views of mooring system anchors.

FIGS. 18 and 19 are, respectively, a perspective view of an OTEC plantand a side view of the associated power cable mooring system.

FIGS. 20A-20C illustrate access procedures for heat exchangers on abarge mounted OTEC plant.

FIGS. 21A and 21B are, respectively, a partial cutaway view and a sideview of a cold water pipe connection.

FIG. 22 is a perspective view of a cold water pipe intake and returnmanifold.

FIGS. 23A-23D illustrate a barge-mounted OTEC plant.

FIGS. 24A and 24B illustrate a joint.

FIG. 25 illustrates a riser extending between a barge and abottom-founded manifold.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Compact OTEC plants can be installed on vessels, e.g., barges, to serveisland or shoreline utilities. Vessel-mounted OTEC plants can providecost-efficient generation of electricity. Such OTEC plant can alsoprovide battery storage system, ancillary services to help stabilize andsustain the utility grid and provide ride-through and ramp up capabilityduring utility grid frequency and voltage fluctuations. Vessel-mountedOTEC plants can operate in normal weather and ocean conditions, andsurvive hurricane conditions (e.g., up to Category 3). Mooring systems,piping systems, and transmission lines can be configured to work withand have low impacts on the local environment.

Infrastructure for a vessel-mounted OTEC plant is configured to providea mooring site for the vessel-mounted OTEC plant in 100 to 300 feet ofwater. The seabed profile for a specific site determines the exactgeometry and arrangement of the system. Typically, at this depth, themooring site is within a mile of shore, yet far enough offshore that thevessel, when present, is visually non-intrusive to observers onshore.This depth range and distance from shore provides easy accessibility forsite surveys, initial plant set up, maintenance, and regular crewrotations. Offshore industrial divers routinely work to this depthsetting mooring anchors, laying submarine power cable to shore andconnecting large diameter pipes, so recovery and restoration ofoperations following a severe storm, such as a hurricane, is reasonablyachievable in terms of time and cost. This design provides for long term(e.g., 25+ years) commercial operability by addressing long termsurvivability of platform connection to essential pipelines andnear-continuous long-term operation with short duration shutdowns basedon controlled operating plans for severe weather conditions. Themanifold solution also reduces project cost by using less expensive HDPEpipe for low-stress long sub-sea pipelines and more expensive flexiblepiping for short run from manifold to platform.

System features are discussed with respect to examples includingbarge-mounted OTEC plants. However, OTEC plants incorporating many ofthe features described can also be mounted on other vessels such as, forexample, small semi-submersibles, submersibles, spars and multi-leggedspars.

Referring to FIGS. 1A, 1B, and 2, an exemplary vessel-mounted OTEC plant100 includes mobile components and fixed infrastructure. The mobilecomponents include, for example, a barge 110 and evaporators 112 andcondensers 114 mounted on the barge 110. The fixed infrastructureincludes, for example, mooring lines 116, mooring buoys 118, mooringsystem anchors 119, and a power cable 120. The following disclosuredescribes the OTEC plant 100 with mobile components attached to theassociated fixed infrastructure. However, the mobile components of theOTEC plant 100 are detachable from the fixed infrastructure. This allowsthe mobile components the OTEC plant to be moved from the mooring site,for example, to perform maintenance in port or seek shelter from severeweather conditions.

The barge 110 is about 300 feet long, 90 feet wide with a variable draftof about 8 to 20 feet. The height above the waterline is about 23 to 35feet. In the OTEC plant 110 illustrated in FIGS. 1A, 1B, and 2, theevaporators 112, the condensers 114, and other associated equipment areinstalled simply mounting the equipment on the barge deck without bargemodifications. For near-coast installations, the barge 110 can bepainted sea blue and white to reduce the visual signature. Other typesand sizes of vessels and other paint schemes can be used.

The barge 110 is oversized in relation to its plant size in order toincrease survivability in heavy storms and to provide space forequipment and personnel. Wind speed in the Caribbean Sea usually remainsbelow 25 knots and wave action is relatively low, so the barge willprovide a stable platform for operation in normal conditions. Similarconditions prevail around the globe between 20N and 20S, with some areasmore susceptible to tsunamis than hurricane. The barge design isanticipated to be capable of surviving a mild tsunami because it will bemoored close to where the pressure wave will build as it rises over theescarpment, and the mooring lines can take a 20 to 22 foot rise.

During exceptional storms and hurricanes, barge motions may exceed the0.2 g acceleration operational limit for equipment and cause the plantto be shut down. In some cases, shock mounts can be included in thevessel design to increase this this limit and go as high as 0.3 g orhigher.

The OTEC plant will be manned at all times except when personnel aremoved ashore during hurricanes. The barge-based plant can remain on siteduring most hurricane scenarios. However, the mooring and pipeattachment configurations enable the barge to be detached and towed intosafe harbor, if deemed necessary, prior to a very severe hurricane, thenreturned to site after the storm passes.

The evaporators 112 and the condensers 114 can be implemented using, forexample, the heat exchange plates, cabinets, and systems described inPCT Applications PCT/US2013/065004, filed Oct. 15, 2013,PCT/US2012/050941, filed Aug. 15, 2012, and PCT/US2012/050933, filedAug. 15, 2012 (attached hereto as an exhibit). In contrast to thesesystems, the evaporators 112 and the condensers 114 in the OTEC plant100 are oriented for horizontal rather than vertical flow. The exemplaryOTEC plant 100 houses a 4-stage hybrid heat exchange cycle as describedin PCT applications PCT/US2011/022115, filed Jan. 21, 2011 (attachedhereto as an exhibit) and PCT/US2013/068894 filed Nov. 7, 2013. Otherheat exchange cycles and plant configurations can also be used in abottom founded OTEC plant.

The evaporators 112 receive warm seawater from warm water inlet piping124, and discharge water to warm water discharge piping 126. Thecondensers 114 receive cooling water from cold water inlet piping 128and discharge used cooling water to cold water discharge piping 130. Inthe barge-mounted OTEC plant 100 illustrated in FIGS. 1A, 1B, and 2, thewarm water inlet piping 124, the warm water discharge piping 126, thecold water inlet piping 128, and the cold water discharge piping 130 areattached to fittings 132 mounted on the sides of the barge 110. Theintake and discharge piping 124, 126, 128, 130 is described below inmore detail.

Vessel-mounted OTEC plants are anticipated to generate 2.5 to 10megawatts of electricity. The power cable 120 transfers generatedelectricity to an onshore interconnection facility tied into the onshoreelectric grid. The power cable 120 for the exemplary OTEC plant 100 is a69 kilovolt 3-phase submarine power cable will be run from the barge 110to the interconnection facility (not shown). In some markets the OTECplant may transmit power to shore via a 34.5 kV 3-phase submarine powercable.

The interconnection facility is set back from the shoreline to reducethe likelihood of flooding and/or wave damage during severe storms. Toprotect both the power cable 120 and the near-shore environment, thepower cable 120 can be installed in a conduit running through an 8-inchto 10-inch diameter hole bored from the interconnection facility,extending under the beach and the near-shore reef. In the exemplary OTECplant 100, the hole and conduit extend for a total distance ofapproximately 1000 feet (e.g., up to 1600 feet) to a breakout point 134(see FIG. 1B) of the bore-hole will be approximately 50 feet (or more)below the ocean surface. Seaward of the breakout point 134, the powercable 120 can be laid on the sea bottom and lightly covered with riprapor seamat. Alternatively, power cable 120 can be laid on the sea bottomand lightly covered with riprap or seamat all the way from the shorelineto where it lifts from the seabed to rise towards the barge 110.

The reef should be as narrow as possible at the selected location inorder to minimize the distance of directional drilling underneath thereef for the power cable routing to the shore. The location should beaway from residential properties and in proximity to the existing powerdistribution grid.

The submarine power cable, about 6 inches in diameter, will be run fromthe barge 110 to the seabed in a lazy wave catenary supported byfloatation collars, touching the seabed at a depth of about 80 feet andrunning along the seabed to the ocean-end of the conduit.

The illustrated OTEC plant 100 has a single barge 110 and associatedmobile equipment and infrastructure. In some systems, a singleinterconnection facility is connected to and controls multiple barges110 and associated mobile equipment and infrastructure.

A battery energy storage system (BESS) can be installed at theinterconnection facility. The BESS will be weather-tight, elevated andanchored against severe storms in accordance with local building codeand good engineering practices. In some installations, a battery energystorage system is installed on the vessel.

Referring to FIGS. 3-7, some vessel-mounted OTEC plants 100 included avessel (e.g., barge 110) that has a moon pool 136 through which seawaterintake and return piping 124, 126, 128, 130 connect to the evaporators112 and condensers 114. The moon pool 136 provides a protected source ofwarm surface water from which the thermal energy is extracted. Locatingthe moon pool 136 in the center of the vessel minimizes the magnitude ofroll, pitch and yaw motion on the pipe connections and also reduces theimpact of wave slap on these connections. The moon pool 136 shields warmwater intake from surface debris and reduces need for screening. Coldwater intake piping inlets can safely penetrate the walls of the moonpool 136 so that they can be below the water line, reducing the headpressure and pumping power requirements.

The seawater intake and return piping 124, 126, 128, 130 run below themain deck keeping the main deck clear for routine operations andmaintenance. The cold water intake piping 128 leads to cold water pumps138 which discharge to inlets of the condensers 114 located above on themain deck. Piping 140 provides a cold water cross connect between thecondensers 114 such that either cold water pump 138 can be used to feedeither or both condensers 114 (see FIG. 4).

The seawater intake and return piping 124, 126, 128, 130 run below themain deck keeping the main deck clear for routine operations andmaintenance. The cold water intake piping 128 leads to cold water pumps138 which discharge to inlets of the condensers 114 located above on themain deck. Piping 140 provides a cold water cross connect between thecondensers 114 such that either cold water pump 138 can be used to feedeither or both condensers 114 (see FIG. 4). Alternatively, a pair ofhigh efficiency vertical turbine pumps lowered directly into the moonpool 136 from a framework above it can be used instead of theillustrated cold water pumps 138. Cold water discharge piping 130 leadsdownward from the barge 110 as described in more detail below.

The warm water inlet piping provides a hydraulic connection between themoon pool 136 and warm water pumps 142 which discharge to inlets of theevaporators 112 located above on the main deck. Piping 144 provides awarm water cross connect between the evaporators 112 such that eitherwarm water pump 142 can be used to feed either or both evaporators 112(see FIG. 4). Alternatively, a pair of high efficiency vertical turbinepumps lowered directly into the moon pool 136 from a framework above itcan be used instead of the illustrated warm water pumps 142. Warm waterdischarge piping 126 leads downward from the barge 110 as described inmore detail below.

The seawater intake and return piping 124, 126, 128, 130 has been sizedfor a hypothetical 5 megawatt barge-mounted OTEC plant. Thishypothetical plant includes 72 to 96 inch diameter primary piping withinthe barge but 48 to 54 inch diameter pipes leading to and from the sea(or the manifold) (see FIG. 5). The large diameter pipes can feed to andfrom smaller diameter pipes as illustrated in FIG. 6. Multiple pipes arean advantage since their reduced size requirement then falls withinstandard off-the-shelf polyethylene pipe sizes. Alternatively, thedischarge piping can be combined in a single large pipe 146 asillustrated in FIG. 7.

In the hypothetical 5 megawatt barge-mounted OTEC plant, the heatexchangers (the evaporators 112 and the condensers 114) are installed incold water and warm water chambers. Each chamber has a supply pump142/138 and a discharge which uses commercial-off-the shelf 72 inchdiameter polyethylene pipe The power turbines, ammonia pumps, andelectrical gear are located on a deck above the water chambers, placingthem about 18 FT above the water surface to protect them from possibleseawater over-wash during storm conditions. Both the warm and cold watersupply lines are cross-connected as described above for redundancy andto facilitate uninterrupted operation while maintenance is performed.In-line filters can be installed in the warm water intake lines but arenot believed to be necessary for the cold water intakes

Referring to FIGS. 8 and 9, a vessel-mounted OTEC plant 100 isconfigured to use bottom mounted manifolds 146, 148 which distribute:cold water flowing to the vessel 110; warm water and cold water beingdischarged from the vessel 110; and cold water being transferred fromthe vessel 110 onshore to provide seawater for air-conditioning. ThisOTEC plant 100 uses substantially the same mooring configurationdiscussed above with respect to FIG. 1.

The OTEC plant 100 illustrated in FIGS. 8 and 9 has substantially thesame barge layout as discussed above with respect to FIGS. 3 and 4. Asdiscussed above, the stresses imposed on the pipe connections to thebarge are reduced by running intake and discharge piping from a moonpool in the center of the vessel 110. The warm water discharge piping,cold water intake piping, and cold water return piping are provided bymultiple, smaller diameter, more riser pipes 150 (e.g., flexible riserpipes) that run from the vessel 110 to concrete OTEC manifold 146 on theseafloor beneath the vessel. A large diameter cold water pipe 152 andseparate warm and cold water return pipes 154 are also attached to theOTEC manifold 146.

Both the cold water and the warm water return pipes 154 run downwardfrom the manifold along the seafloor in parallel to a depth, forexample, of 400-500 feet. The discharge ends of the cold water returnpipe and the warm water return pipe can be banded side-by-side andnozzled and/or louvered up and away from the sea floor so that the flowsmix, reducing the likelihood of either thermal/nutrient contamination ofthe surface seawater or erosion of the sea floor. The cold water and thewarm water return pipes 154 are anchored to maintain their positionsrelative to each and to the seabed. A plume study by Makai OceanEngineering for the US Department of Energy titled, “Modeling thePhysical and Biochemical Influence of Ocean Thermal Energy ConversionPlant Discharges into their Adjacent Waters,” published in October 2012and available on-line, shows that mixing the flows of return water canbe beneficial.

A weighted collar or several weighted collars 156 are attached to thesesmaller diameter riser pipes such that the smaller diameter riser extendto the seafloor-mounted manifold in a lazy wave fashion that acts as ashock absorber to decouple the forces and motions between the pipes andthe vessel. The multiple riser pipes 150 in each piping system alsoprovide redundancy which increases operational reliability andflexibility. The riser pipes 150 can be manufactured of high-densitypolyethylene (HDPE) and are commercially available in the requireddiameters.

The cold water pipe 152 for the OTEC plant 100 runs from the OTECmanifold 146 along the sea floor to a depth of where water temperaturesare consistently about 40 degrees Fahrenheit (e.g., ˜approximately 3,800feet on the north shore of Grand Cayman Island) and has a 96-inch innerdiameter. The intake end 158 (see FIG. 9) of the cold water pipe 152 ismodified (e.g., screened) to prevent the entrainment of any large marineanimals by having an average inlet velocity of 0.5 feet per second. Thecold water pipe 152 can be formed as described in PCT applicationPCT/US2013/065098 filed on Oct. 15, 2013. However, the manifold 146 isfixed in position and the cold water pipe 152 is disposed on the seabedand, optionally, covered with riprap. As the cold water pipe 152experiences little to no stress at the connection to the bottom foundedstructure, lower cost HDPE for pipes material with up to 100 yearservice life can be used, Such pipes are currently commerciallyavailable.

In the illustrated OTEC plant 100, warm and cold water being dischargedby the system are mixed at the outlet of the bundled warm/cold waterreturn pipes 154. This mixing dilutes nutrients and lowers temperaturespresent in the warm water discharge. The bundled warm/cold water returnpipes 154 run downward from the OTEC manifold 146 on the sea floor to adepth near the bottom of the photic zone (e.g., depth of ˜400-600 feet).This approach avoids the turbidity and sea floor erosion issues that canbe caused by pointing a separate warm water discharge straight down fromthe vessel 110 in relatively shallow water.

The depth at which dissolved oxygen is greatest, and where pelagic fishtend to school is referred to as the mixing layer in the ocean. Datacollected over many months using the University of Hawaii's autonomousunderwater data collection devices, SeaGlider 1 and SeaGlider 2, revealthe mixing layer to be between 130 and 160 meters deep. The nutrientrich, cold water pumped from 3,700 feet or deeper is denser than thesurface seawater as will tend to descend rather quickly until the wateris fully assimilated in the surrounding ocean water. In the OTECprocess, the water temperature will be raised by about 10 degrees F. butthere will be no chemical changes. The warm surface water will exit theOTEC system about 10 degrees F. cooler than it entered. It needs to bereturned to the ocean at a depth that assures that it will not rise andcontaminate the surface water thereby affecting the power plant outputcapability. By returning the cold deep seawater and the warm surfaceseawater at the same depth, several meters above the mixing layer, theOTEC plant works to rapidly restore balance to nature by a) mixing theoutput so that the condenser return water mixes with and cools theevaporator return water, b) the nutrients in the condenser return waterare diluted by the evaporator return water, and c) the now denser mixedreturn water will tend to descend more rapidly as it assimilates intothe surrounding ocean water. This assimilation will occur in the mixinglayer where the nutrients, now diluted, are expected to enhance theproduction of food for pelagic fish, thereby increasing their number inthe immediate area.

The discharge ends 160 of the bundled warm/cold water return pipes 154are directed upwards away from the seabed and can include a nozzle or adiffuser. This approach can avoid the turbidity and sea floor erosionissues that can be caused by laying the return pipes on the sea floor todischarge parallel the sea floor. Some OTEC plants 100 are implementedwith a combined warm/cold water return pipe rather than separate coldwater and warm water return pipes 154.

A similar approach is used to provide condenser effluent from the OTECplant 100 to be used onshore for seawater air conditioning (SWAC). TheSWAC manifold 148 is positioned between the vessel 110 and the shorelinein approximately 24 to 50 feet of water. A condenser effluent line 162routes a portion of the condenser effluent produced by the OTEC plant100 to the SWAC seachest manifold 148. A pipe or pipes extends from theSWAC seachest manifold 148 to a pipe manifold that is located onshore. Abooster pump on the OTEC plant and powered by a variable frequency drivereceiving a control signal from the manifold on shore maintains constantdelivery pressure at the manifold.

A hypothetical SWAC system was designed that included a single, 20-inchinner diameter HDPE pipe 162 extending from the vessel 110 to the SWACmanifold 148 in approximately 24 to 30 feet of water. Two 12-inch innerHDPE pipes 166 extend from the SWAC manifold 148 to a concrete dischargebasin 164 planted in ground onshore. The two 12-inch inner HDPE pipes166 pass under the beach in bore holes made by horizontal directionaldrilling. Pumps co-located with the basin 164 transfer water from theSWAC manifold 148 to the basin 164. Further pumps and piping are used totransfer cold water to facilities being cooled.

The platform will be moored in 150 to 300 feet of water, which isrelatively shallow (mooring in thousands of feet of water is presentlyconsidered routine). A standard eight-point moor will be employed. Eachmooring line is attached to a stand-off buoy for ease of attachment anddetachment. Alternatively, each mooring line is attached to a constanttension mooring winch mounted on the deck of the OTEC plant. Mooringanchors will likely be gravity, embedment or drilled, depending on seafloor composition and emplacement costs. All options are well understoodin the industry. Sea floor composition will be determined throughon-site surveys including core samples.

Referring to FIG. 10, the vessel 110 has small knuckleboom cranes 168installed so that the barge can be moored/unmoored without externalassets. Terminal mooring interface is via simple deck-mounted chainplates. These onboard cranes should also be helpful in general cargohandling and transfer during normal operations.

Referring to FIG. 11, the mooring system dynamically adjusts to changingsea level as may be necessary to compensate for the storm surgeassociated with severe storms or tsunamis. Storm surge is a rise in sealevel produced by a combination of the wind, tidal, and pressureeffects. As it is typically reported for hurricanes, storm surge usuallyincludes the added surface waves. A storm surge of 20 feet will submergea land mass which is 20 feet above sea level. Storm surge affects afixed mooring differently than do open water waves. A mooring can bedesigned to accommodate the vertical motion of the moored barge by theaction of the tension bar buoys. While this accommodation does put smalladditional loads on the mooring gear, storm surge does not create ahorizontal load on the barge as do wind, waves, and current. As thestorm surge arrives, the barge 110 lifts from its initial position to arelatively higher position (e.g., barge 110′). The mooring buoys 118also lift to a relatively higher position (e.g., buoys 118′). Themooring buoys 118 rotate and are partly submerged as lifting of thebarge (110>110′) takes slack out of the mooring lines. The rotation andsubmergence of the mooring buoys acts to increase the effective lengthof the mooring legs as shock absorbers to reduce surge loads.

FIG. 12 is a perspective view of a mooring system and cold water pipeconfiguration for a barge-mounted OTEC plant. This specific interface ofthe mooring and water pipe systems is configured for a proposed locationon the coastal shelf off of Cape Eleuthra. The mooring legs can be ofquite different lengths and angles as required to interface with thespecific bottom topographies. The cold water pipe 152 is secured/mooredusing gravity anchors 170 of 4000 LB submerged weight spaced every 130FT. Cost is reduced by using magnetite sand (specific gravity=5) insteel boxes to achieve the required mass. Since the cold water pipe isslightly buoyant at 15 pounds per foot of pipe, weighted collars 172 areutilized to achieve the catenary curves shown. The weighted collars canbe, for example, concrete anchors 172′ (see FIG. 13) or fabricated steelgravity anchors 172″ (see FIG. 14).

FIGS. 15-17 are schematic views of mooring system anchors 119′, 119″,119′″. The anchors will be more reliable if placed, for example, inmudstone or coral. The mudstone is similar in properties to sandstoneand the coral is similar in properties to limestone. Both substrates arevery suitable for properly designed embedment anchors.

The anchors 119 can be installed, for example, using an explosiveembedment method, a bottom sitting hydraulic pile driver device, and/ora gravity driver system with a heavy, retrievable torpedo weight todrive the anchor in. Small barge-mounted cranes of multi-hundred toncapacity are in wide use in coastal and offshore work and readilyavailable to install the anchors 119. Some barge cranes simply use aland-based crawler crane installed on the barge. A 100-ton crane couldalso be installed on the barge 110 temporarily, or permanently and usedfor operational cargo transfers.

FIGS. 18 and 19 are, respectively, a perspective view of a barge mountedOTEC plant 100, and a side view of the associated power cable mooringsystem. The exemplary power cable mooring is a buoy-supported lazy wavedesign that includes buoyancy collars 172. Several buoyancy collars canbe grouped together to form a virtual buoy 176. For typical sites, thepower cable run to shore will be in relatively shallow water and thepower cable 120 will be typically protected and anchored by rock cover.Routing through coral reefs or beach littorals will be via directionallydrilled tunnels. The barge 110 has eight chain legs running to tensionbar buoys 118. These buoys 118 provide some load attenuation in themooring legs and also maintain the mooring system in place if the bargeis disconnected. The mooring legs continue with multiple lines of 2-inchdiameter polyethylene (PE) line, either four or three per leg asrequired to meet load requirements. The PE mooring lines each terminatewith a single emplaced embedment anchor as described above with respectto FIGS. 15-17.

Referring to FIGS. 20A-20C, power plant systems are readily supported onthe upper decks of the HX chambers since the chambers are positivepressure and the structure is commensurately strong. The heat exchangerplates are assembled as modules 178 of 84 plates. These modules arereadily handled by a small forklift. The modules are installed in a rack180 which slides in and out of the water chambers 182 (e.g., evaporator112/condenser 114), providing access to the heat exchange modules. Allhusbandry of the heat exchange system is accomplished from the deck ofthe barge using conventional material handling equipment.

The heat exchange modules can be removed from the racks for inspection,repair or replacement. The simple nature of the water chambers allowsfor all module-to-module plumbing to be accomplished inside the chamberprior to installing the hatches. Thus, the hatches do not requirethrough-fittings for the ammonia piping.

FIGS. 21A and 21B are, respectively, a partial cutaway view and a sideview of a cold water pipe connection valve 184 (a Dredge Yard 48″ IDquick-connect ball valve fabricated for the dredging industry). The 48″diameter matches the pump inlet diameters and is adapted up to the 63″pipe ID or larger. In some systems, e.g., systems that do not includethe seabed installed manifold, the cold water pipe can be connected tothe barge pumps with a limited motion ball joint as the cold water pipeconnection valve 184. This joint is principally to isolate the coldwater pipe from short period, small amplitude roll and pitch motions.The larger and slower motions of surge, sway, and heave are absorbed inthe loop of the flexible high density polyethylene (HDPE) cold waterpipe.

In systems with the seabed manifold, the small diameter water pipes willconnect to the barge pumps and discharges with commercial off-the shelfball joints. This joint is principally to isolate the pipe from shortperiod, small amplitude roll and pitch motions of the barge. The largerand slower motions of surge, sway, and heave are absorbed in the loop ofthe flexible PE pipe located between the barge and the pipe buoys.

FIG. 22 is a perspective view of a cold water pipe intake and returnmanifold 146. The manifold 146 includes o-rings and retainer blocs. Theend of the pipe is prepared with o-rings and retainer ring and then theblocs are bolted to the outside of the receptacle, sealed in themanifold

FIGS. 23A-23D illustrate a barge 110 that is 206 feet long, 139 feetwide, and 28 feet in height. The barge 110 includes a moon pool 136located between evaporators 112 and condensers 114. The principalequipment on the deck is the heat exchanger system. The HX arrays aresupported in racks and enclosed in water chambers that allow for theflow of warm and cold water over the interconnected HX cartridges toaccomplish the gasification and condensation of the ammonia workingfluid contained within the cartridges. The deck installations alsoinclude ammonia storage tanks, habitation modules, and cargo handlinggear.

In this embodiment, the evaporators 112 and the condensers 114 arelocated at the corners of the barge 110 and systems with movingmechanical parts such as generators and turbines are located towards thecenter of the barge 110. FIG. 23B illustrates the location of suchsystems. The power plant machinery is located amidships port andstarboard of the moon pool. These spaces contain the four turbines,ammonia pumps, and associated controls and switch gear that comprise thepower generation system. In addition to personnel stairwells and thegantry crane hatches, the machinery spaces will also be served byfreight elevators. The machinery is located as close to the center ofthe vessel as possible where the acceleration due to motion is theleast. Scale model testing shows these accelerations to be less than 0.2g even in the worst storm conditions. This configuration places highmass components with few or no moving parts on the portions of the barge110 that experience the highest accelerations as the barge 110 pitchesand/or rolls.

The heat exchanger cartridges are interconnected in arrays which arethemselves installed in racks which slide in and out of the waterchambers. The ammonia piping is connected inside the chambers before thechamber side hatches are installed and feeds down to the power plantsystem below decks. The HX arrays are serviced by sliding racks out ofthe chambers where individual arrays can be serviced or replaced. Thedeck arrangement allows the cold water chambers and warm water chambersto share a maintenance deck area and minimize the overall platform size.The HX array racks are slid out of the water chambers through removableclosure hatches. The HX arrays, comprising 84 Heat Exchanger cartridgespermanently installed in a housing cocoon, can then be removedindividually.

The moon pool serves as the connection point between the platform andthe cold and warm water supply and return pipes. The use of a moon poolallows this critical connection to be located at the point of leastplatform motions and to be protected from wave impacts and collisions.It also allows the piping runs to be well away from the mooring systemchains. The incorporation of an organic gantry crane over the moon poolassists in the installation and maintenance of the water piping andseawater pump systems. The gantry crane also services two large deckhatches located over the machinery spaces and allows for machinery andsupplies to be moved from the platform deck to the below-decks spaces.The crane the ability to overhang the platform deck and to offloadgeneral cargo from supply boats of convenience.

The platform perimeter bulwark is intended to protect the deck fromgreen water during storm conditions and also to screen the deckmachinery and activities from view of off-platform persons and providefor an esthetic visual signature. The bulwarks have removable panels atthe corners for installing the mooring chains. The bulwarks incorporatesliding hatch amidships so that cargo can be easily transferred fromsupply boats to the barge 110. The bulwarks have drainage gaps at theirdeck connections.

The mooring chains extend downward from bottom corners of the barge 110rather than to can buoys. Tests using 1/35 scale models indicate thatthis configuration can be used in low wave environments such as, forexample, on the leeward side of islands. The can buoy mooringconfiguration provides additional flexibility and may be required inhigher wave environments such as, for example, on the windward side ofislands.

FIG. 23C illustrates the arrangement of pumps and piping. The coldseawater and warm seawater vertical axis pumps are located in drychambers extending out from the moon pool wall with connections to theunderwater piping and intakes. Space has been allocated for pumpisolation valves and manifolds that will allow for redundancy in sewaterservice. The steel distribution piping runs below deck and feedsdirectly into the water distribution plenums located at the ends of theHX chambers. The return piping is fed directly from the water returnplenums located at the ends of the HX chambers. The piping manufacturerscan supply segment-welded piping turns as required for the installation.

FIG. 23D illustrates the cold and warm water external piping. Theexternal supply and return pipes are connected to the internal pumps andpipes through welded fittings at the moon pool wall. Flexible, strongsuction dredge hose then connects to a seabed manifold located directlybeneath the moon pool. The concrete manifold merges the flexible hoseinto the large seabed-supported 84″ diameter cold water supply and coldand warm water return pipes. The seabed pipe can be double wallspiral-rib type HDPE.

Rather than rising from the OTEC manifold 146 to the barge 110 in a lazywave as illustrated in FIGS. 8 and 9, each riser pipe 150 is separatedinto two sections that form a loop. The two sections are joined bytension/shear/torsion (TST)-constrained flexible joints 186 developedfor this system. An embodiment of these joints is discussed in moredetail below with respect to FIGS. 24A and 24B. This pipingconfiguration accommodates platform motions relative to the fixed seabedmanifold. Platform motions during the 99^(th) percentile operationalweather are expected to be on the order of a few feet insurge/sway/heave and tenths of a degree in roll/pitch/yaw. Thepre-tensioning of the mooring chain system significantly amelioratesplatform motions during all weather conditions. The maximum surge andsway motions expected during hurricane conditions are 15 FT and maximumheave is 10 FT. The flexible connection system must accommodate thesemotions without undue loading on the piping and piping connections. Thepiping support platform are guyed to the platform so that the loads aretaken by the cables and structure and not by the vertical steel pipesconnecting to the platform.

FIGS. 24A and 24B show a TST-constrained flexible joint 186 limitingtension and torsion, respectively. In this embodiment, theTST-constrained flexible joint 186 includes a flexible rubber element188 between two flanges 190 to contain the seawater and to resist jointloads in compression. The rubber element 188 is surrounded by a meshformed of flexible chains 192 that resist joint loads in tension, shear,and torsion. The chains are interwoven and attached by bolts screwedinto the flanges 190. The number and orientation of the chains cancontrol the directions and extent of joint flexibility. The rubberelement 188 is molded in a desired shape based on the joint applicationand the chains are oriented based on desired directions of jointflexibility.

The TST-constrained flexible joints 186 can provide significantversatility in designing riser configurations for attaching the barge110 to the OTEC manifold 146. FIG. 25 shows another example riserconfiguration. At this site, the seafloor drops very steeply (almostvertically) beyond 450 feet depth. The distance between the barge andcold water at 3,800 feet deep is quite short compared to some otherlocations. The riser pipe assembly is articulated by 90-degree elbowsconnected to TST-constrained flexible joints 186. The number of risersdepends on the number of pipes needed for the flow based on the size ofthe plant power output.

All references mentioned herein are incorporated by reference in theirentirety.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, OTEC plant can have three or more evaporator or condenserchambers, three or more warm water or cold water pumps, two or moreintake and discharge seachest manifolds, or two or more cold watereffluent SWAC seachest manifolds and three or more pipes to two or morepipe manifolds on shore; OTEC barge with mooring lines rising directlyand attaching to mooring winches on the barge or rising to mooring cansbefore lines run to and attach to the barge; no overall deck covering sothat the silhouette of the OTEC plant against the horizon is staggeredby the images of the deck-mounted structure. Accordingly, otherembodiments are within the scope of the following claims.

1. An offshore power generation system comprising: (a) a floatingportable platform comprising; (1) one or more OTEC heat exchange units;(2) one or more turbine generators; (3) a water intake and dischargesystem; (4) a mooring system; and (b) a fixed manifold comprising: (1)one or more cold water intake connections in communication with a coldwater pipe; (2) one or more cold water discharge connections incommunication with the water intake system of the floating platform viaan intermediate cold water conduit, wherein each cold water dischargeconnection is detachable from the intermediate cold water pipe; (3) oneor more Warm Water discharge connections in communications with thewater intake system of the floating platform via an intermediate warmwater conduit, wherein each warm water discharge connection isdetachable from the intermediate warm water pipe.
 2. (canceled)
 3. Thesystem of claim 1 wherein each OTEC heat exchange unit is connected tothe water intake and discharge system to allow for substantially linearflow of cold water and hot water across the OTEC heat exchange unit. 4.The system of claim 3 wherein each OTEC heat exchange unit comprises aplurality of heat exchange plates positioned in the flow path of thecold water supply.
 5. The system of claim 3 wherein each OTEC heatexchange unit comprises a plurality of heat exchange plates positionedin the flow path of the warm water supply.
 6. The system of claim 3wherein an OTEC working fluid flows through an interior passage of oneor more heat exchange plates, each heat exchange plate surrounded by andin the flow path of the cold or warm water supply.
 7. The system ofclaim 1 wherein each OTEC heat exchange unit comprises four cascadingheat exchange zones.
 8. The system of claim 7 wherein each cascadingheat exchange zone arranged to facilitate horizontal flow of the cold orwarm water supply.
 9. The system of claim 1 wherein the water intake anddischarge system comprises a warm water supply pump and a cold watersupply pump.
 10. The system of claim 1 wherein the water intake anddischarge system includes a warm or cold water discharge pump.
 11. Thesystem of claim 1 wherein one or more discharge pipes are incommunication with the discharge of the water intake and dischargesystem.
 12. The system of claim 1 wherein the intermediate cold waterpipe is detachable from the water and intake discharge system.
 13. Thesystem of claim 11 wherein the discharge pipe is detachable from thewater intake and discharge system.
 14. The system of claim 11 whereinthe terminal end of the warm water discharge pipe is at a depth between25 and 500 feet (e.g., between 250 and 500 feet).
 15. The system ofclaim 11 wherein the terminal end of the cold water discharge pipe is ata depth between 25 and 500 feet.
 16. The system of claim 11 wherein theterminal end of the warm water and cold water discharge pipes dischargewater at a depth having a temperature within 10 degrees Fahrenheit ofthe ambient water.
 17. The system of claim 11 further comprising: (a) acold water discharge pipe in communication with the water intake anddischarge system and the fixed manifold; (b) a warm water discharge pipein communication with the water intake and discharge system and thefixed manifold; wherein the warm and cold water discharge are mixed inthe fixed manifold and discharged from the manifold at a temperaturewithin 10 degrees Fahrenheit of the ambient water.
 18. The system ofclaim 17 further comprising a mixing nozzle in communication with thewarm and cold water discharge.
 19. The system of claim 1 wherein thecold water pipe is coupled directly to the water intake and dischargesystem via a cold water pipe connection.
 20. The system of claim 1further comprising an auxiliary cold water supply exiting the fixedmanifold and supplying an auxiliary system.
 21. The system of claim 20wherein the auxiliary system is a shore based air conditioning system.22-25. (canceled)